1. Field of the Invention
The present invention relates to a beam scanning apparatus of an electrophotographic color printer.
2. Description of the Related Art
FIG. 1 shows a general electrophotographic color printer. Referring to the drawing, an electrophotographic color printer includes a photoreceptor such as a photoreceptor belt 1, a beam scanning apparatus 30 for forming an electrostatic latent image by exposing the photoreceptor belt 1 to light, and developing units 21, 22, 23, and 24 for developing the electrostatic latent image.
The photoreceptor belt 1 circulates around guide rollers 3. The electrostatic latent image remaining on the photoreceptor belt 1 is removed by a reset unit 2. An image record surface of the photoreceptor belt 1 is exposed to the beam emitted from the beam scanning apparatus 30.
The respective developing units 21-24 develop images of different colors, e.g., yellow, magenta, cyan, and black. The beam scanning apparatuses 30 are positioned at the upstream side of each of the respective developing units 21-24 and develop the electrostatic latent image by colors. The developed image is dried by a drying unit 8 and then transferred via a transfer roller 9 to a paper 10 passing between the transfer roller 9 and a fusing roller 11.
FIG. 2 shows a conventional beam scanning apparatus which is adopted in the above electrophotographic color printer to expose the photoreceptor to light. Referring to the figure, the conventional beam scanning apparatus 30 includes a light source 31, a beam deflector 34 for deflecting light emitted from the light source 31, and an f-.theta. lens 37 for correcting an error of the light deflected by the beam deflector 34.
Also, a focusing lens 33 for focusing the divergent beam emitted from the light source 31 is provided between the light source 31 and the beam deflector 34. A mirror 38 for changing a direction of a path of light is provided between the beam deflector 34 and the photoreceptor (not shown). Here, the focusing lens 33 determines the size of an optical spot formed on the photoreceptor.
The beam deflector 34 includes a motor 35 and a rotary polygonal mirror 36 which is rotated by the motor 35. The beam input to the beam deflector 34 is deflected according to an angle made between a reflection surface of the rotary polygonal mirror 36 and the input beam.
In the beam scanning apparatus 30 having the above structure, the photoreceptor is exposed to light by a main scanning by the beam deflector 34 and a sub-scanning by the movement of the photoreceptor perpendicular to the direction of the main scanning.
However, the structure of the beam scanning apparatus 30 which includes the rotary polygonal mirror 36 and the motor 35 is complicated. Further, in case of a color printer, the beam scanning apparatus 30 must be provided for each color to form a color image, thereby increasing the size of the apparatus. Also, the position of the deflected beam is affected by the wobble generated during rotation of the rotary polygonal mirror 36.